The invention relates to an A/D conversion device having an analog input intended to receive an analog input voltage and a digital output intended to supply a digital signal resulting from the conversion of the analog input voltage, comprising an A/D converrer having an analog input, connected to the input of the device and moreover, via a storage capacitor, to a fixed DC potential source, and having an output constituting the output of the device, and a control module, provided with an analog comparator receiving a differential signal at the input, referred to as control signal and constituted by a first signal which is a signal having a predetermined fixed value and a second signal which is a signal representative of the input signal of the converter, said control module supplying a signal from its output allowing adjustment of the voltage at the terminals of the storage capacitor and being activated when the analog input voltage has a reference threshold.
Such a device is used, inter alia, in apparatuses for digitally processing images. The control module is used for auto-adjustment of the DC component in the signal supplied.
An A/D conversion device as described in the opening paragraph is known from U.S. Pat. No. 5,371,552. In the device described in this document, the control module comprises an analog comparator which performs a comparison between the analog signal at the input of the A/D converter and a reference voltage produced on the basis of voltages which feed the resistance ladder of this converter.